Real time determination of oil film thickness by neutron imaging and scanning

Examination of damaged surfaces of projectiles and targets after ballistic tests has shown that a fine globular knobbled structure, previously assumed to result from adiabatic shear fracture, is present on a wide range of metallic materials. Experiments have now shown that this structure is associated with rubbing of surfaces at high velocities and occurs as a result of the flash melting of ridges on the grooved surfaces which is due to frictional heating. On the basis of surface energy it is found that break-up of the surface, modelled as a series of ridges, into discrete globules or knobbles is energetically favourable. Estimates of the temperatures attained in various projectile and target materials during penetration and the thickness of the melted films are consistent with observations and measurements on actual projectile and target specimens.     

Thermal diffusivity of nonflat plates using the flash method

The flash method is the standard technique to measure the thermal diffusivity of solid samples. It consists of heating the front surface of an opaque sample by a brief light pulse and detecting the temperature evolution at its rear surface. The thermal diffusivity is obtained by measuring the time corresponding to the half maximum of the temperature rise, which only depends on the sample thickness and thermal diffusivity through a simple formula. Up to now, the flash method has been restricted to flat samples. In this work, we extend the flash method to measure the thermal diffusivity of nonflat samples. In particular, we focus on plates with cylindrical and spherical shapes. The theoretical model indicates that the same expression for flat samples can also be applied to cylindrical and spherical plates, except for extremely curved samples. Accordingly, a curvature limit for the application of the expression for flat samples is established. Flash measurements on lead foils of cylindrical shape confirm the validity of the model.     

The measurement of thermal conductivities using the photothermal deflection method for thin films with varying thickness

This study considers non-contact methods that obviate the causes of measurement error, such as thermal contact resistance and the unnecessary destruction of samples. Among the methods, the photothermal deflection method has been adopted and developed to measure the thermal conductivities of thin-film materials. To apply the developed method for thin films, bi-layered materials are manufactured by depositing the film on Corning 7740 glass plates. The study also investigates the optimal modulation frequency, as related to the thermal diffusion length of the sample, for measuring thermal conductivities of thin films.. Aluminum, TiO₂, and Si₃N₄ films with micro/nanometer thickness were selected as the objects for measurement; the thermal conductivities of these films were experimentally measured. Samples of thickness ranging from 1 μm to 200 nm were prepared to measure the variations in thermal conductivities with thickness. It was observed that the thermal conductivity in submicroscale films decreased as the thickness was reduced.     

Measurement of thermal diffusivity using deformation gradient and phase in the photothermal displacement technique

As technology advances with development of new materials, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. The measurement of thermal properties can be done in a non-contact way using photothermal displacement spectroscopy. In this work, the thermal diffusivity was measured by analyzing the magnitude and phase of deformation gradient. We proposed a new data analysis method based on the real part of deformation gradient as the pump-probe offset value. As the result, compared with the literature value, the measured thermal diffusivities of materials showed about 3% error.     

Discrete thickness optimization of an automobile body by using the continuous-variable-based method

Design optimization of an automobile body for dynamic stiffness improvement is presented. The thicknesses of plates consisting of a monocoque body of an automobile are employed as design variables for optimization whose objective is to increase the first torsional and bending natural frequencies. By allotting one design variable to each plate of the body, compared to previous works based on element-wise design variables, the design space of optimization can be reduced to a large extent. Because the present optimization is based on continuous-variable-based algorithms, considering manufacturability of the optimized result, the converged values of plate thicknesses should be approximated to commercially available discrete values. A new straightforward thickness discretization scheme considering design sensitivities and employing a subsequent reduced optimization problem is proposed. The validity of the proposed thickness discretization scheme is verified through numerical experiments.     

The theoretical study of the measuring thermal diffusivity of semi-infinite solid using the photothermal displacement

A method of measuring the thermal diffusivity of semi-infinite solid material at room temperature using photothermal displacement is proposed. In previous works, within the constant thickness of material, the thermal diffusivity was determined by the magnitude and phase of deformation gradient as the relative position between the pump and probe beams. In this study, however, a complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in semi-infinite solid materials. The influence of parameters, such as, radius and modulation frequency of the pump beam and the thermal diffusivity, was studied. We propose a simple analysis method based on the zero-crossing position of real part of deformation gradient and the minimum position of phase as the relative position between two beams. It is independent of parameters such as power of pump beam, absorption coefficient, reflectivity, Poisson’s ratio, and thermal expansion coefficient.     

On the methodology of the thyroid epithelial cell thickness determination

The average thickness of the thyroid epithelial cells may be determined either directly or indirectly. By the direct or caliper method, this thickness is overestimated as a result of which its empirical value must be divided by a correction factor K_d. By the indirect method, on the other hand, the thickness of the thyroid gland epithelium is calculated as the ratio of the double volume density of the epithelium to the sum of the inner and the outer surface density of the epithelium; in this case the sought for thickness value is underestimated and must consequently be multiplied by a factor K_i. Both correction factors are algebraically defined. Their values are calculated and graphically represented as a function of the thyroid activation index (the ratio between the volume density of the epithelium and the colloid) for the range from 0·1 to 100. The validity of the theoretical interpretation of the discrepancy between the values obtained for the average thickness of the thyroid epithelium by the direct and the corresponding values obtained by the indirect method, is empirically tested. It is shown that by the introduction of appropriate correction factors the difference between the results obtained by each method can be reduced. These improved direct and indirect methods for determining the wall thickness of a hollow sphere seem to lend themselves to being used in the stereological analysis of other biological, perhaps even non-biological materials of similar structure.     

Laser flash method for measuring thermal conductivity of liquids-application to low thermal conductivity liquids

A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal conductivity. The sample liquid was sandwiched in between a small thin metal disk and a sample holder. When the laser beam is absorbed in the front surface of the metal disk, the temperature of the disk quickly rises about 2 K and heat then flows downwards through the sample liquid as one-dimensional heat flow. The thermal conductivity of liquid can be obtained from the temperature fall of the disk without employing any reference materials and also without measuring the thickness of the sample liquid layer. Thermal conductivities of water and toluene near room temperature were measured by this method with a mean deviation of 2.6%. This laser flash method may be applied to the measurement of the thermal conductivity of liquids such as molten salts at elevated temperatures.     

Direct determination of ultrathin section thickness using latex particles

A method is proposed to determine ultrathin section thickness by means of noncentral sections obtained from latex spheres. The resulting spherical segments provide the parameters necessary to calculate very simply the section thickness without further treatment. The method is illustrated by an example using the grid-sectioning technique and could be generalized to classical microtomy.     

表面加工多晶硅薄膜热扩散系数在线测试结构

基于目前已有的真空桥式薄膜热扩散系数测试结构和测试方法，综合考虑辐射、对流以及向衬底的传热等因素的影响，从而使得本文设计的测试结构和提取方法更具有实际价值。文中通过分析两个长度不同，但宽度与厚度相同的梁在相同加热电流下的瞬态电阻变化特性，来提取多晶硅薄膜的热扩散系数。同时利用有限元分析软件ANSYS进行了模拟分析，分析表明模拟提取值与理论值较好地吻合，从而验证了模型建立的正确性，说明该方法能够实现对多晶硅薄膜热扩散系数的在线提取，且具有较高的测试精确度。     

Device for characterization of thermal effusivity of liquids using photothermal beam deflection

We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the sample under study. An optical angle sensor is used to measure the laser deflection providing a simple and experimental arrangement. We demonstrate its principle and a simple procedure to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.     

A modified formula for accurate determination of three‐dimensional birefringence of fiber using modified subfringe integration method

The development of the use of interferometric techniques in the study of the optical properties of materials encouraged many researchers to work on the derivation and development of the theoretical considerations and the equations used in the calculations of those properties. The form of these equations depends on the technique used and the cross section of the sample, and also on the method of calculating the optical path difference of light across the sample studied. A modified formula to calculate the three‐dimensional birefringence distribution of the fiber, without the need to determine the refractive indices of the fiber in the parallel and perpendicular directions, was presented. The phase distribution of the simulated and experiment interferograms was obtained using subfringe integration method. The results obtained from the new method were compared with the calculated results of a well‐known method (Z method) and the figures presented showed that the results of the two methods were close to each other.     

反射系数法微波检测热障涂层厚度的实验研究

为了保证热障涂层的隔热效果,对热障涂层的厚度进行了微波无损检测.检测中探头选用R281A带法兰矩形波导探头,工作频率范围为26.5 ～ 40 GHz.仿真计算利用CST微波工作室(computer simulation technology-microwave studio)软件进行.实验结果表明,在26.5～40 GHz工作频率范围内,反射系数的相位差能良好地表征热障涂层的厚度.并且在高频率段时可以达到相位差变化l°,热障涂层的厚度变化约8μm的分辨率.在28.5～29.1 GHz工作频率范围内,反射系数的幅值也能表征热障涂层的厚度.实验结果与仿真结果基本吻合.     

Determination of thermal plume thickness using thermocouple cross correlation coefficient decay

A methodology to measure the thickness of a thermal boundary layer by cross correlating the signal from thermocouples is presented. It is shown that measurement of temperature, velocity, and boundary layer thickness is achievable using a single sensor utilizing three thermocouples rather than the typical two thermocouples used in the cross correlation velocimetry technique discussed in literature. The methodology is validated using experiments performed in two laboratory scale devices: a heated turbulent jet and a variable diameter natural gas burner. Experimental measurements are compared with theoretical calculations, and uncertainty in the measurement is discussed.     

Vibration analysis of piezoelectric FGM sensors using an accurate method

In this study, free vibration analysis of moderately thick smart FG annular/circular plates with different boundary conditions is presented on the basis of the Mindlin plate theory. This structure comprised a host FG plate and two bonded piezoelectric layers. Piezoelectric layers are open circuit therefore this plate can be used as a sensor. According to power-law distribution of the volume fraction of the constituents, material properties vary continuously through the thickness of host plate while Poisson's ratio is set to be constant. Using Hamilton's principle and Maxwell electrostatic equation yields six complex coupled equations which are solved via an exact closed-form method. The accuracy of the frequencies is verified by the available literature, finite element method (FEM) and the Kirchhoff theory. The effects of plate parameters like boundary condition and gradient index are investigated and significance of coupling between in-plane and transverse displacements on the resonant frequency is proved.     

Investigation of the technique of ultrasonic thickness control using the EMA method

Experimental studies of the electromagnetic-acoustic (EMA) method for controlling the thickness of sheets, metalware, equipment, and pipelines were performed. New methods for the measurement of ultrasonic thickness that provide thickness control without cleaning the contact surface of a tested object and without using contact greases, as is required when using conventional contact ultrasonic transducers, are shown. On the basis of these studies and the experience of ultrasonic thickness gauging (USTG) by the contact and EMA methods, a USTG technology that uses the EMA method has been developed.     

An extrapolation method for the determination of Cliff-Lorimer kAB factors at zero foil thickness

An extrapolation method is proposed to be useful for the determination of the Cliff-Lorimer k_AB factor at zero foil thickness. The method consists of measuring k_AB factors as a function of the measured foil thickness, t_M, and extrapolating the relationship toward t_M=0. The intersection between the extrapolated line and the ordinate of t_M=0 gives (k_AB)₀ which is free from the effect of absorption. The straight line extrapolation that can be achieved by a linear-least squares method is particularly developed to eliminate arbitrariness introduced in the extrapolation process. The extrapolation method is applied to data available in the literature. It is shown that the method yields the (k_AB)₀ factors compatible with those predicted from the theoretical calculation. It is also shown that this method can circumvent several problems which make it complex and difficult to determine accurate values of the absorption-free k_AB factors. Using the straight line extrapolatioin, it is possible to estimate the degree of the thickness overestimation which arises when the foil thickness is measured by the contamination spot separation (CSS) method. Validity of the straight line extrapolation is further discussed.     

Characterization of the topography and thickness of gallium thin films by scanning tunneling microscopy

Scanning tunneling microscopy (STM) was employed to characterize the topography of 32 and 4 µm thick gallium films; thicknesses that have not yet been addressed. The STM images revealed submicron grains on both surfaces although a reduced grain density was observed on the thinner film. The granular structure may be explained by a thin gallium oxide layer that acted as an elastic membrane against liquid gallium underneath that expanded during freezing of the sample. We also believe that the same gallium oxide layer is also responsible for an intriguing effect that appears as soon as the tungsten tip lands on the gallium film: the onset of continuous regular z-oscillations of the tip even at rest. This is an effect that we believe has not been previously reported in the literature. We have also demonstrated, for the first time, a new thickness determination method for the gallium film based on an STM image obtained during the solid-to-liquid phase transition.